To control a technical installation, a process control system is normally used which includes a number of components which specialize in particular tasks and are installed at various locations within the technical installation, for example in a power plant for generating electric power.
In this case, the process control system usually has a hierarchic structure involving a plurality of levels. At a field level, the signals which arise during operation of the technical installation and describe the operating state of installation components are detected and control signals are sent to actuating elements for the installation components.
At an automation level, the control functions used to operate the installation are implemented in a plurality of programmable logic controllers (PLCs), for example. During implementation, a specific piece of control software developed for control tasks is usually used (e.g. step 5, step 7 etc.), which can be executed only on particular types of CPUs which are in turn operated by a specific operating system. The automation level receives signals from the field level and sends commands to the field level. In this case, the connection between the field and automation levels can be in the form of individual wiring of each pickup and/or of each actuating element to corresponding inputs and outputs for the automation level, but it is also possible to use a field bus system with a particular, usually very specific transmission protocol for this purpose.
An operator control and monitoring level forms a man/machine interface which an operator can use to operate the technical installation and to obtain information therefrom. In this case, the operator obtains, for example on a screen in a computer system in the form of process images, graphical information about the installation state and he can use, by way of example, a mouse and/or a keyboard in the computer system to input operating commands into the computer system. The operator control and monitoring level is often connected to the automation level by way of a power plant bus system, in which case the bus system is in the form of an optical fiber system, for example, and is operated using a specific transmission protocol.
The computer system for the operator control and monitoring level usually includes a specific piece of operator control and monitoring software installed thereon. The control software is usually produced directly at the automation level using a programming device which is connected to the automation devices (PLCs) and which is used to generate the “target code” for the corresponding automation device, and/or using a separate engineering system which, by way of example, is formed by a computer on which modules are selected from a library and are connected to one another graphically, for example, in order to provide a desired control function. Subsequent compilation generates the target code from the graphical function diagram, and said target code is then loaded on the desired automation device (PLC) at the automation level and is executable.
The use of such a known process control system thus requires the use of hardware and software components respectively tailored to particular tasks. The operator control and monitoring software is not executable on the automation devices. Further, conversely, the control software is not executable on the operator control and monitoring system's computer system.
To operate a technical installation, it is thus necessary to use various systems in parallel beside one another which are not suitable for taking on tasks from one of the other systems. In addition, the systems also cannot be arranged at almost any physical distance from one another, since the connection between them, usually a bus system or individual wiring, cannot be extended arbitrarily. Further, such an extension—if it is at all possible to implement—would be very expensive and susceptible to error.
Conventional process control systems are thus usually arranged in strictly hierarchic form, with each level of the hierarchy using systems which are specifically matched to the respective task, such as the aforementioned PLC or the aforementioned automation bus systems (for example the Sinec H1 bus from Siemens or the Profibus). The systems are then also usually operated with software packages developed specifically for automation technology. Since, as already mentioned, the maximum reachable distance at which the components of a known process control system can be installed away from one another is limited, it is usually the case in practise that virtually all the components of the process control system are installed within the technical installation.
Such a known process control system is very expensive, since specific hardware and software is used which still needs to be configured and parameterized by experts for use in the technical installation. In addition, it is possible to diagnose, maintain and optimize components and functions of the process control system practically only in situ. Furthermore, known process control systems have only very limited control options from locations which are outside the technical installation (to this end, known process control systems usually have a separate system, such as a gateway, with this specifically configurable gateway often being able to be used to perform only a portion of the control tasks externally; in this case, it is frequently necessary to couple systems having different transmission protocols with a great deal of involvement).
In addition, an operator needs to obtain specific training in order to be able to operate the process control system.
The strict hierarchic structure of a known process control system can take the following form, for example:
At least one automation device (e.g. a PLC) at the automation level stores control programs produced in a specific programming language, and these control programs are executed there. By way of example, the automation device stores the control algorithm for operating a motor.
The operator control and monitoring system stores the graphical process images, for example, in which the current process measurement and state values are overlaid as dynamic image components, and command areas are provided in which the user can send an operator control command (e.g. start up/set in motion; prescribe nominal value etc.) using a mouse click or a keyboard input, for example. The operator control command is then transmitted, for example using a power plant bus system, to the automation level, where it is then executed by a control program running on the automation device, this involving the control program driving actuating elements in the technical installation and reading in measurement values from sensors, for example.
In the case cited by way of example, the operator control and monitoring system has the motor's process image stored in it, for example. Further, the current operating states of the motor (e.g. the speed, power, operating time, temperature etc.), which are sent to the operator control and monitoring system by the automation system using the power plant bus system, are overlaid in said process image. The user is then able to click on a command button on the screen or to press a key, for example, and thereby to start the motor, to stop it or to request a higher power etc. (in which case the control program associated with the respective command is executed in the automation system).
An engineering system for the process control system engineers the process control system's control functionality, for example, by calling control modules from a software library, connecting them to one another and supplying them with parameter values, for example on a graphical user interface. The resultant control programs put together from a plurality of control modules are then converted (compiled) to that target code which is then loaded on a target device at the automation level and is executable there. The engineering system is also able, by way of example, to create and parameterize the process images with their static and dynamic image components; the process control system is thus configured and engineered using the specialized engineering system.
Furthermore, there can additionally be a separate diagnosis system which is used to monitor the operating state of the technical installation particularly the critical operating states.
In summary, it can be said that, in order to perform its tasks, a known process control system requires a multiplicity of specialized, heterogeneous subsystems in which usually specific hardware and software are used. Operating and configuring such a heterogeneous overall system are therefore very complex, and the implementation and purchase costs of such systems are very high. In addition, such process control systems are not very flexible, inter alia on account of the high level of specialization of its subsystems.